conditional images

I uploaded a patch to the tracker for initial conditional image support.
I didn't go so far as to increase the conditionals capabilities, just
enough to let an image change be triggered by a WPS element (i.e. when
moving from a VBR file to a CBR file, or when shuffle is
enabled/disabled). Anyone interested in this can find it at the URL below.

Here's hoping someone wants it enough to add to CVS so I don't have to
keep patching my local CVS tree! :D